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Certain HVAC applications use air filtration systems incorporating several stages of filtration. In a first stage, a prefilter is used to trap particles in the range of 5 microns and greater. In a second stage, a second or main filter is used to trap smaller particles in the range of 3 to 5 microns, and so on depending on the application. The main filter assembly includes sections of filter media that have been arranged in an accordion fashion to from a row of aligned V shapes. Adjacent sections are held in place by longitudinal bridging strips that bridge adjacent end faces. The frame and bridging strips are typically formed from a molded or extruded plastic material. Other stages of filtration may be provided downstream of the main filter assembly.
In these multi-stage filter systems, the prefilter cannot be butted directly against the main filter to prevent blinding off of the main filter, which would increase the resistance to air flow and decrease service life. The prefilter is thus typically provided as a separate assembly that is located upstream of the main filter assembly. The prefilter assembly accordingly takes up a whole stage of filtration.
The present invention provides a system for butting up filters together while keeping a sufficient separation, preferably 1 inch, between them necessary for optimum performance. The present invention accordingly eliminates a stage of filtration and reduces the volume taken by the additional stage of filtration.
In a further embodiment, the present invention also provides a filtration system incorporating edge banding on adjacent V-shaped sections of filter media in the main filter assembly. The edge banding comprises strips of a strong sheet media, for example, a nonwoven polyester material or extruded, calendered polymers or plastics. The strips are preferably adhesively bonded along the edges of adjacent V-shaped sections.
The edge banding eliminates the need for extruded plastic bridging strips, which increase the pressure drop across the filter. Accordingly, the present invention results in a lesser pressure drop across the filter and is simpler and less costly to manufacture.